Bug-type feedback is encouraged. Of particular interest is mount and umount, as I've enabled entirely new implementations based purely on libmount. No, this won't be the default for Arch's actual 2.21 package, but I've been using it myself and haven't found any show stoppers yet. That said, you should expect to find bugs of varying severities and perhaps slightly different behavior, but I'm very much interested in finding these bugs now so that we can perhaps enable this for 2.22.